Abstract
In this paper, we examine the sensitivity of the three-top quark production at the LHC to the top quark flavor-changing neutral currents (FCNC) as well as the sensitivity of the four-top production to the strong and weak dipole moments of the top quark. Upper limits at $95\%$ CL on the branching fractions of $\mathcal{B}(t\rightarrow qX)$, where $X = g, Z, \gamma, H$ and $q=u,c$, are set by performing an analysis on three-top events in the same-sign dilepton channel. We consider the main sources of the background processes and a realistic detector simulation is performed at the center-of-mass energy of 14 TeV. In the second part of this work, based on the recent upper limits which have been set on the four-top quark cross section by the ATLAS and CMS collaborations from 13 TeV data, we constrain the top quark strong and weak dipole moments. The bounds on the top quark dipole moments are presented using the future LHC prospects for four-top quark cross section measurement.
Highlights
In proton-proton collisions at the LHC, mostly top quarks are produced in pair via strong interaction [1,2] or singly via weak interactions [1,2]
We examine the sensitivity of the three top quark production at the LHC to the top quark flavor-changing neutral currents (FCNC) as well as the sensitivity of the four top production to the strong and weak dipole moments of the top quark
Due to the very small production rate of the three and four top quark in the standard model (SM) which are few fb at the LHC, the observation of these processes is quite challenging. Both the three and four top processes give rise to interesting set of final states depending on various top quarks decay modes
Summary
In proton-proton collisions at the LHC, mostly top quarks are produced in pair via strong interaction [1,2] or singly via weak interactions [1,2]. Searches for fpouffiffir top quark production using the Run I data set at s 1⁄4 8 TeV have been performed by both the CMS [5,6] and ATLAS [7,8] experiments, with no observed excess of data above the background expectation. Based on an integrated luminosity of 19.8 fb−1 in pp collisions at a center-of-mass energy of 8 TeV, upper limits on Bðt → qγÞ and Bðt → qZÞ through FCNC single-top-quark production in association with a photon or a Z boson are obtained [66,67]. Using the data collected at the center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb−1 by the ATLAS detector, the observed upper limits on the branching fractions are found to be [71]: Bðt → ugÞ < 4.0 × 10−5; Bðt → cgÞ < 2.0 × 10−5: ð4Þ.
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